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MG MGB Technical - Is my fuel tank working correctly?

When i fill my 72 BGT up, i always fill it up so that there is fuel lying in the neck - thus i can be sure i have a full tank (don't trust my gauge particularly).

However, the frst few miles result in a very strong petrol smell in the car which can be overpowering to passengers, however i am used to it and so don't notice as much (this worries me as it is something i think i should not be "getting used to").

yesterday when i opened the fuel cap on a near empty tank, i heard a loud hiss. Something i have not heard before, although it was rather warm yesterday (can't remember when it was last warm here!).

That got me thinking, i remember some mention of hissing and ineffective fuel breather pipes or something.

Can anyone enlighten further on this and/or tell me where the fuel breather pipes are so i can check their function? I don't want to be ina dangerous situation....

TIA as always ~PHIL
Phil

Phil,

UK cars rely on a vented filler cap to relieve pressure in the tank.

The fuel smell is coming from poor seals on the filler neck pipe - I bet the rubber hose is loose or perished.

Chris Betson

My GT suffered in the same way with a not quite tight filler neck. That said, I did read in the original manual a warning about never filling up to the neck, especially in warm weather. Tightening the jubilee clips and not filling so full has allowed me to breathe fresh air again, having let the car air for a few days.
Steve Postins

I always get that hiss whne i open my tank and when it is low it bends in wards and makes a clanking niose. My tank is aonly 4 months old. I bought a new fuel cap from the mg club beliving that it was just the breather in my fuel cap not working. Well the same hiss and tanks compressing still happens particulary on a hot day and with a near empty tank. What i do now is try and drive with the tank between qualter and 3 quater full and it does not seem to have that hissing when i open the tank.
jim

I bought a fixer upper MGB several months ago. It had been modified by taking most of the required polution equipment off the engine etc. I drove the car around town and to work with no apparent trouble. I finally decided to retire. That led to a trip of several hundred miles to my home. The fuel guage had always read empty so I did not pay it attention. At about the 250 mile mark on the trip home, the engine sputtered and died in the middle of nowhere and of course at night. the one thing that I did notice as that the fuel guage now read full. I took the cap of the tank and heard a loud swoosh of air and the distint sound of a fuel tank unfolding. It seems that on short trips (under 50 miles) the tank would have a chance to recover to normal pressure but on a long trip the tank would bend up lifting the fuel level sensor toward the full range. When enough suction was created in the tank to over power the fuel pump the engine would quit. I solved the problem temporarily by drilling a small, repeat small hole in the cap and alway made sure that the hole way on the up side when I replaced the cap. After that -no problem. I of course have to now add this problem to the restoration list.
J.F. Rowles 111

From what i understand the USA cars are meant to have breathers on the tank not just the cap as UK cars do.
jim

Jim that is true.However the person who removed most of the pollution equipment just pinched off the inputs to the canisters and left them.Aha no vent.
J.F. Rowles 111

Phil
If you can't fix it, I suggest you get a no smoking sign.
Sorry, just my sense of humour!
Sounds like the breather hole is blocked, the hiss is caused by vaccum.
Dek
D.M Bicknell

Phil
i was in the process of writting a similar question. i to have have had a heavy smell of fumes in the car just after filling up. i cheched the seals on the locking cap (which i have found out should be vented to stop implosion to the tank)which appeared to be in reasonable condition. i also checked to face of the filler pipe this appeared to be in reasonable condition. on saturday which was freakishly hot for the uk i purchased a new cap when i returned home to fit it petrol was pouring out of the car. i changed the cap and still had the same leakage. a closer inspection of the filler pipe face with a straight edge did not show any deflections. the next obvious stage is to replace filler pipe or am i being nieve and is there a simple and obvious solution to this fuel leakage. or is it a case that i cant see the wood for the trees.
mick
M Curley

I bought one of those mg rover replacement fuel caps becuase i had the same breather problem with my fuel cap. The new fuel cap supplied did no seem to breath any better i was wondering is it possble to change to an american style set up with the breather on the tank ( i am thinking of chaning my tank again anyway as i want an orginal style with bafflers to stop the petrol rolling about and upsets stability on tight bends.
ed

This thread was discussed between 23/06/2003 and 24/06/2003

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